1. Field of the Invention
The present invention relates in general to Ethernet Passive Optical Network (EPON) communications, and in particular to managing upstream data traffic allocations in an EPON.
2. Background of the Invention
As EPON moves into mass deployment, more people rely on this technology for network access. Because network users are using more services relying heavily on network communication, such as voice over IP and video on demand, there is growing demand on the performance of an EPON.
In an EPON, there are multiple Optical Network Units (ONUs) and one Optical Line Termination (OLT). The OLT typically resides at the Central Office (CO) and connects the EPON to one or more external networks. Each of the ONUs typically resides at a subscriber's home and connects the subscriber to the EPON. Alternatively, an ONU can be connected to multiple subscribers.
The OLT controls how data is communicated in the EPON. All data communications through the EPON must go through the OLT, including those between two ONUs of the EPON. The downstream traffic from the OLT is standard Ethernet traffic. An entity that transmits and receives data to and from the OLT within each ONU is called a logical link and is identified by a unique logical link identifier (LLID). A local link can maintain several local queues for different traffic priorities. For example, voice packets should be prioritized ahead of data packets (which may contain lower priority web or peer-to-peer traffic), therefore voice packets are placed in a queue with higher priority than the queue holding data packets. Because there are multiple ONUs in an EPON, two or more logical links from different ONUs may transmit data upstream to the OLT at the same time, causing a collision in the upstream traffic. To prevent collisions from happening, the EPON follows the control protocol described in IEEE 802.3ah.
The control protocol described in IEEE 802.3ah uses a Multi-Point Control Protocol (MPCP) to manage the upstream traffic of an EPON. According to the MPCP, each logical link reports the upstream transmission demands of its local queues to the OLT. The OLT divides the upstream transmission bandwidth into upstream transmission windows and allocates the upstream transmission windows to logical links upon request. To allocate the transmission windows, the OLT uses a Dynamic Bandwidth Allocation (DBA) algorithm. Each of the logical links in turn assigns allocated upstream transmission bandwidth to its local queues based on the demands and priorities of the local queues.
This approach is inadequate in providing quality of service to the EPON subscribers. Quality of service is a measure of performance for a transmission system that reflects its transmission quality and availability of service. The traditional approach can result in inefficient upstream bandwidth allocation, especially when a logical link supports multiple Ethernet ports. For example, when one Ethernet port generates continuous high priority upstream transmission demands, it may take over most of the bandwidth allocated to the logical link. In such a case the lower priority upstream transmission demands of the same Ethernet port and the upstream transmission demands of the other Ethernet ports of the same logical link are left to share the remaining limited transmission window.
Another problem of the traditional approach is that the allocation mechanism cannot guarantee a minimum bandwidth to a particular stream (e.g., guaranteeing the necessarily bandwidth to maintain a quality VOIP connection). Also, because the OLT allocates upstream bandwidth on a per-logical link basis only, leaving the assignment of upstream bandwidth to local queues to the logical link, it is difficult to configure or reconfigure the EPON to provide and maintain a quality of service to the subscribers.
Some applications attempt to improve the quality of service by allocating multiple logical links to one ONU, each associated with an Ethernet port. Because the OLT allocates bandwidth based on logical links, an Ethernet port with its own logical link can be guaranteed a minimum upstream bandwidth by the OLT according to a DBA algorithm. But because each logical link reports transmission demands to the OLT each DBA cycle, a large amount of logical links within an EPON would increase upstream overhead (e.g., the upstream bandwidth used by logical links to transmit REPORT messages to the OLT). This in turn could consume a substantial portion of the upstream traffic, leaving the subscribers with insufficient upstream bandwidth.
Therefore, there is a need for a system and process that provides enhanced upstream data traffic management for an EPON by improving the mechanism for allocating upstream bandwidth to queues of a logical link.